A typical mobile communication network comprises one or more base stations. In particular, such a mobile communication network may be a UMTS, a 3GPP Long-Term-Evolution (LTE) or 3GPP Long-Term-Evolution-Advanced network (LTE-A). The base stations may be a NodeB (NB) or enhanced NodeB (eNodeB, eNB), especially a Home NB or Home eNB (H(e)NB). Low transmission power base stations may have access restrictions. The 3GPP therefore has specified the closed subscriber group (CSG) services for example using home base stations H(e)NBs or for deploying enterprise networks, for example office solution formed from multiple pico base stations. A CSG is a private base station or a private network (multiple base stations) providing services to only a closed subscriber group (CSG) of users.
Compared to conventional eNBs for HeNB an important additional feature is the ability to select and indicate eNB access type by physical layer configuration. The two standardized types of cells are open (normal) ones (OSG, Open Subscriber Group) and CSG (Closed Subscriber Group) ones and the access types are called open and closed. According to 3GPP specification physical layer notification can be done by selecting physical cell IDs defined for open or closed access and to signal on the BCCH (broadcast control channel) of a wide area cell which physical cell IDs indicate open and which physical cell IDs indicate closed access. In an open subscriber group (OSG) scenario, any terminal or subscriber is served by the OSG node (for example eNB) and in a closed subscriber group (CSG) scenario, the CSG node, for example HeNB, serves only a limited number of terminals, which may be only subscribers that are allowed to access the given CSG node.
If the CSG network is operated at the same carrier frequency as an OSG or non CSG network, interference from CSG nodes to OSG nodes may arise. With CSG enabled for example the access of visiting user equipment to a HeNB or a pico NB is prevented. However on the other hand wide area dead zones are caused by the downlink interference from the CSG nodes, for example HeNB, which makes it impossible to the visiting user equipment to access neighboring OSG nodes, for example wide area networks, when visiting macro user equipments (UEs) are located close to a CSG HeNB or pico NB.
There may be a need for providing a reliable and computational inexpensive method for adapting a downlink transmitting power of a first base station adapted for serving a closed subscriber group, which reduces interferences between base stations.